Rhizoctonia

Rhizoctonia is a type of fungi. They have long filaments called mycelia and a root like structure consisting of food reserves, called sclerotia. Rhizoctonia species eat through a process called saprotrophic nutrition, as the filaments (mycelia) absorb decayed organic matter through the cell wall. The species may resort to plant pathogeny, meaning that it can sometimes cause crop diseases. Some Rhizoctonia species live on the roots of orchid plants and exhibit a mutually beneficial relationship with them during orchid germination.

The term Rhizoctonia (meaning “root killer”) was first used by Augustin Pyramus de Candolle to describe the species Rhizoctonia crocorum, which causes violet root rot in carrots. It was found that Rhizoctonia solani also causes significant plant diseases, affecting grass, seeds, potatoes, cereals, sugar beet, cucumber, rice and many others.

 Disease 
When this type of fungus begins to grow on a plant the infected area decays rapidly, leading to brown and red lesions below the soil-line. If the disease develops, these lesions enlarge to form sunken cankers that can cut through the plant root and stem. Other symptoms include plants wilting in the middle of the day and damping off.

 Characterisation 
Since Rhizoctonia don't produce many spores, they are characterised by their hyphae. The hyphae are responsible for producing branch filaments at right and acute angles. Some hyphae are specialised with compact cells called miliolid cells. These cells form strong structures called sclerotia, this strength allows these fungi to survive extreme conditions.

There are two groups of classification based on the number of nuclei (cell compartment storing genetic material) within the hyphae cells. The two groups are binucleate (two nuclei) and multinucleate (more than two nuclei) Rhizoctonia.

A further classification into groups is based on the ability of hyphae to fuse together, by a process called Anastomosis.

 References 

Category:Botany
Category:Fungi